This is the first comprehensive molecular investigation of the genus Lamium L. We have addressed phylogenetic relationships and presumed allopolyploid speciation by use of nuclear (NRPA2, 5S-NTS) and chloroplast (matK, psbA-trnH, rps16, trnL, trnL-F, trnS-G) DNA sequence data. Nuclear and chloroplast data were incongruent, and nuclear data showed better correlation with morphology. Bayesian and parsimony phylogenetic results show that (1) Lamium galeobdolon is sister to all remaining Lamium species; (2) Wiedemannia is nested within Lamium; (3) L. amplexicaule is polyphyletic; (4) most tetraploids are of hybrid origin; (5) L. amplexicaule var. orientale is allotetraploid; and (6) Mennema’s (1989) infrageneric classification is not corroborated by molecular data. Based on the molecular results, and taking morphology into account, we suggest resurrection of two species: L. aleppicum and L. paczoskianum.